1. Field of the Invention
The present invention relates to a spin valve thin film magnetic element, a thin film magnetic head, and a method of manufacturing the spin valve thin film magnetic element. Particularly, the present invention relates to a spin valve thin film magnetic element comprising a synthetic ferrimagnetic free layer comprising two magnetic layers with a nonmagnetic intermediate layer provided therebetween.
2. Description of the Related Art
Magnetoresistive magnetic heads include a MR (Magnetoresistive) head comprising an element exhibiting a magnetoresistive effect, and a GMR (Giant Magnetoresistive) head comprising an element exhibiting a giant magnetoresistive effect. In the MR head, the element exhibiting the magnetoresistive effect has a single layer structure comprising a magnetic material. On the other hand, in the GMR head, the element exhibiting the magnetoresistive effect has a multilayer structure in which a plurality of materials are laminated. Of several types of structures creating the giant magnetoresistive effect, a relatively simple structure exhibiting a high rate of change in resistance with an external magnetic field is a spin valve thin film magnetic element.
Recently, high-density magnetic recording has been increasingly required, and a spin valve thin film magnetic element adaptable to high density recording has increasingly attracted attention.
A conventional spin valve thin film magnetic element is described with reference to the drawings. FIG. 19 is a schematic sectional view showing a conventional spin valve thin film magnetic element 101, as viewed from the magnetic recording medium side, and FIG. 20 is a schematic sectional view of the spin valve thin film magnetic element 101, as viewed from the track width direction.
A reproducing thin film magnetic head comprises the spin valve thin film magnetic element 101, and shield layers formed above and below the spin valve thin film magnetic element 101 with gap layers provided therebetween. In addition, a recording inductive head may be laminated on the reproducing thin film magnetic head.
The thin film magnetic head is provided at the trailing side end of a floating slider together with the inductive head to form a thin film magnetic head for detecting a recording magnetic field of a magnetic recording medium such as a hard disk, or the like.
In FIGS. 19 and 20, the Z direction coincides with the movement direction of the magnetic recording medium, the Y direction coincides with the direction of a leakage magnetic field from the magnetic recording medium, and the X1 direction coincides with the track width direction of the spin valve thin film magnetic element.
The spin valve thin film magnetic element 101 shown in FIGS. 19 and 20 is a bottom-type single spin valve thin film magnetic element in which an antiferromagnetic layer 103, a pinned magnetic layer 104, a nonmagnetic conductive layer 105, and a free magnetic layer 111 are laminated in turn.
In FIGS. 19 and 20, reference numeral 100 denotes an insulating layer made of Al2O3 or the like, and reference numeral 102 denotes a base layer made of Ta (tantalum) or the like, and laminated on the insulating layer 100. The antiferromagnetic layer 103 is laminated on the base layer 102, the pinned magnetic layer 104 is laminated on the antiferromagnetic layer 103, and the nonmagnetic conductive layer 105 made of Cu is laminated on the pinned magnetic layer 104. Furthermore, the free magnetic layer 111 is laminated on the nonmagnetic conductive layer 105, and a protecting layer 120 made of Ta or the like is laminated on the free magnetic layer 111.
The layers from the base layer 120 to the protecting layer 120 are laminated in turn to form a lamination 121 having a substantially trapezoidal sectional shape having a width corresponding to the track width.
The pinned magnetic layer 104 is made of, for example, Co, and laminated in contact with the antiferromagnetic layer 103. An exchange coupling magnetic field (exchange anisotropic magnetic field) occurs in the interface between the pinned magnetic layer 104 and the antiferromagnetic layer 103 so that the magnetization direction of the pinned magnetic layer 104 is pinned in the Y direction.
The free magnetic layer 111 comprises first and second free magnetic layers 110 and 108 with a nonmagnetic intermediate layer 109 provided therebetween. The first free magnetic layer 110 is provided on the protecting layer side of the nonmagnetic intermediate layer 109, and the second free magnetic layer 108 is provided on the nonmagnetic conductive layer side of the nonmagnetic intermediate layer 109.
The thickness t1 of the first free magnetic layer 110 is larger than the thickness t2 of the second free magnetic layer 108.
The first free magnetic layer 110 is made of a ferromagnetic material such as a NiFe alloy or the like, and the nonmagnetic intermediate layer 109 is made of a nonmagnetic material such as Ru or the like.
The second free magnetic layer 108 comprises an anti-diffusion layer 106, and a ferromagnetic layer 107, both of which are made of a ferromagnetic material. For example, the anti-diffusion layer 106 is made of Co, and the ferromagnetic layer 107 is made of a NiFe alloy. The first free magnetic layer 110 and the ferromagnetic layer 107 are preferably made of the same material.
The anti-diffusion layer 106 is provided for preventing mutual diffusion between the ferromagnetic layer 107 and the nonmagnetic conductive layer 105 to increase the GMR effect (xcex94MR) produced in the interface with the nonmagnetic conductive layer 105.
Assuming that saturation magnetizations of the first and second free magnetic layers 110 and 108 are M1 and M2, respectively, the magnetic thicknesses of the first and second free magnetic layers 110 and 108 are M1xc2x7t1 and M2xc2x7t2, respectively.
Since the second free magnetic layer 108 comprises the anti-diffusion layer 106 and the ferromagnetic layer 107., the magnetic thickness M2xc2x7t2 of the second free magnetic layer 108 is the sum of the magnetic thickness of the anti-diffusion layer 106, and the magnetic thickness of the ferromagnetic layer 107.
The free magnetic layer 111 is formed to satisfy the relation M1xc2x7t1 greater than M2xc2x7t2 between the magnetic thicknesses of the first and second free magnetic layers 110 and 108.
Actually, the saturation magnetization of Co which constitutes the anti-diffusion layer 106 is higher than that of the NiFe alloy which constitutes the ferromagnetic layer 107 and the first free magnetic layer 110, and thus the thickness t1 of the first free magnetic layer 110 is set to be extremely larger than the thickness t2 of the second free magnetic layer 108 in order to establish the relation M1xc2x7t1 greater than M2xc2x7t2.
The first and second free magnetic layers 110 and 108 are antiferromagnetically coupled with each other. Namely, when the magnetization direction of the first free magnetic layer 110 is oriented in the X1 direction shown in the drawings by bias layers 132, the magnetization direction of the second free magnetic layer 108 is oriented in the direction opposite to the X1 direction.
Since the magnetic thicknesses of the first and second free magnetic layers 110 and 108 have the relation M1xc2x7t1 greater than M2xc2x7t2, magnetization of the first free magnetic layer 110 remains so that the magnetization direction of the entire free magnetic layer 111 is oriented in the X1 direction. At this time, the magnetic effective thickness of the free magnetic layer 111 is (M1xc2x7t1xe2x88x92M2xc2x7t2).
In this way, the first and second free magnetic layers 110 and 108 are antiferromagnetically coupled with each other so that the magnetization directions thereof are antiparallel to each other, and the magnetic thicknesses thereof have the relation M1xc2x7t1 greater than M2xc2x7t2. Therefore, the first and second free magnetic layers 110 and 108 are brought into a synthetic ferrimagnetic state.
As a result, the magnetization direction of the free magnetic layer 111 crosses the magnetization direction of the pinned magnetic layer 104.
Furthermore, the bias layers 132 made of, for example, a Coxe2x80x94Pt (cobalt-platinum) alloy, are formed on both sides of the lamination 121. The bias layers 132 are formed for orienting the magnetization direction of the free magnetic layer 111 in the X1 direction to put the free magnetic layer 111 in a single magnetic domain state, suppressing Barkhausen noise of the free magnetic layer 111.
In FIGS. 19 and 20, reference numeral 134 denotes a conductive layer made of Cu, or the like.
Furthermore, bias base layers 131 made of a nonmagnetic material, for example, such as Cr, are provided between the bias layers 132 and the insulating layer 100, and between the bias layers 132 and the lamination 121.
Furthermore, intermediate layers 133 made of a nonmagnetic material, for example, Ta or Cr, are provided between the bias layers 132 and the conductive layers 134.
In the spin valve thin film magnetic element 101, when the magnetization direction of the free magnetic layer 111, which is oriented in the X1 direction, is changed by a leakage magnetic field from the recording medium such as a hard disk, the electric resistance changes with the relation to magnetization of the pinned magnetic layer 104 which is pinned in the Y direction so that the leakage magnetic field from the recording medium is detected by a voltage change based on the change in electric resistance.
Since the free magnetic layer 111 comprises the first and second free magnetic layers 110 and 108 which are antiferromagnetically coupled with each other, the magnetization direction of the whole free magnetic layer 111 is changed with an external magnetic field of small magnitude, thereby increasing the sensitivity of the spin valve thin film magnetic element 101.
Particularly, the magnetic effective thickness of the free magnetic layer is (M1xc2x7t1xe2x88x92M2xc2x7t2), and thus the effective thickness can be decreased by controlling the thicknesses of the first and second free magnetic layers 110 and 108. Therefore, the magnetization direction of the free magnetic layer 111 is easily changed with an external magnetic field of small magnitude, thereby increasing the sensitivity of the spin valve thin film magnetic element 101.
In the conventional spin valve thin film magnetic element 101, the thickness t1 of the first free magnetic layer 110 is set to be extremely larger than the thickness t2 of the second free magnetic layer 108 in order to establish the relation M1xc2x7t1 greater than M2xc2x7t2.
However, the thickness of the entire free magnetic layer 111 increases as the thickness tl of the first free magnetic layer 110 increases to increase a shunt (a so-called shunt loss) of a sensing current, thereby causing a problem in which the rate of change in resistance of the spin valve thin film magnetic element 101 cannot be sufficiently increased.
Also, the sensitivity of the spin valve thin film magnetic element is increased by decreasing the effective thickness (M1xc2x7t1xe2x88x92M2xc2x7t2) of the free magnetic layer 111. However, when xcex94MR is increased by decreasing the effective thickness while maintaining the relation M1xc2x7t1 greater than M2xc2x7t2, a magnetic field with which spin flopping transition occurs in the free magnetic layer 111, i.e., a spin flopping field, is decreased.
The spin flopping field represents the magnitude of an external magnetic field when the magnetization directions of two magnetic layers are not antiparallel to each other with an external magnetic field applied.
Namely, a decrease in the spin flopping field of the free magnetic layer 111 causes the antiferromagnetic coupling between the first and second free magnetic layers 110 and 108 to be easily broken by the bias magnetic fields from the bias layers 132, and thus the magnetization directions of the first and second free magnetic layers 110 and 108 are not oriented in antiparallel directions. Therefore, the ferrimagnetic state of the free magnetic layer 111 cannot be maintained to possibly cause a decrease in the rate of change in resistance (decrease in reproduced output), and asymmetry of reproduced waveform.
The present invention has been achieved in consideration of the above situation, and an object of the present invention is to provide a spin valve thin film magnetic element and a manufacturing method therefor, which are capable of increasing sensitivity and the rate of change in resistance while stably maintaining the ferrimagnetic state of a free magnetic layer. Another object of the present invention is to provide a thin film magnetic head comprising the spin valve thin film magnetic element and producing high reproduced output.
In order to achieve the objects, the present invention has the following construction.
A spin valve thin film magnetic element of the present invention comprises an antiferromagnetic layer, a pinned magnetic layer formed in contact with the antiferromagnetic layer so that the magnetization direction is pinned by an exchange coupling magnetic field with the antiferromagnetic layer, a nonmagnetic conductive layer in contact with the pinned magnetic layer, and a free magnetic layer in contact with the nonmagnetic conductive layer, wherein the antiferromagnetic layer comprises any one of alloys represented by the formula Xxe2x80x94Mn (wherein X represents one element selected from Pt, Pd. Ru, Ir, Rh, and Os), and alloys represented by the formula Xxe2x80x2xe2x80x94Mn (wherein Xxe2x80x2 represents at least one element selected from Pt, Pd, Cr, Ni, Ru, Ir, Rh, Os, Au, and Ag), and the free magnetic layer comprises first and second free magnetic layers with a nonmagnetic intermediate layer provided therebetween, wherein the magnetization directions of the first and second free magnetic layers are antiparallel to each other, the first and second free magnetic layers are brought into a ferrimagnetic state, and the thickness of the second free magnetic layer provided on the nonmagnetic conductive layer side is larger than the thickness of the first free magnetic layer.
In the spin valve thin film magnetic element, of the two magnetic layers which constitute the free magnetic layer, the second magnetic layer provided on the nonmagnetic conductive layer side is thicker than the first free magnetic layer so that the magnetic thickness of the second free magnetic layer is larger than that of the first free magnetic layer.
Therefore, the spin flopping field of the free magnetic layer is increased, and thus the antiferromagnetic coupling between the first and second free magnetic layers can be stably maintained to maintain the ferrimagnetic state of the free magnetic layer, thereby increasing the sensitivity of the spin valve thin film magnetic element.
The spin flopping field is preferably higher than the bias magnetic fields from the bias layers.
Since the first and second free magnetic layers are antiferromagnetically coupled with each other to be put into the ferrimagnetic state, a difference between the magnetic thicknesses of both magnetic layers corresponds to the magnetic effective thickness of the free magnetic layer.
Therefore, the effective thickness of the free magnetic layer is decreased by appropriately controlling the thicknesses of the first and second free magnetic layers so that the magnetization direction of the free magnetic layer can be changed with an external magnetic field of small magnitude, thereby increasing the sensitivity of the spin valve thin film magnetic element.
In addition, the magnetic effective thickness of the free magnetic layer can be decreased while the thickness of the entire free magnetic layer is increased to some extent, thereby increasing the sensitivity of the spin valve thin, film magnetic element without significantly decreasing the rate of change in resistance.
In another aspect of the present invention, a spin valve thin film magnetic element comprises an antiferromagnetic layer, a pinned magnetic layer formed in contact with the antiferromagnetic layer so that the magnetization direction is pinned by an exchange coupling magnetic field with the antiferromagnetic layer, a nonmagnetic conductive layer in contact with the pinned magnetic layer, and a free magnetic layer in contact with the nonmagnetic conductive layer, wherein the antiferromagnetic layer comprises any one of alloys represented by the formula Xxe2x80x94Mn (wherein X represents one element selected from Pt, Pd, Ru, Ir, Rh, and Os), and alloys represented by the formula Xxe2x80x2xe2x80x94Mn (wherein Xxe2x80x2 represents at least one element selected from Pt, Pd, Cr, Ni, Ru, Ir, Rh, Os, Au, and Ag), and the free magnetic layer comprises first and second free magnetic layers with a nonmagnetic intermediate layer provided therebetween, wherein the magnetization directions of the first and second free magnetic layer are antiparallel to each other, the first and second free magnetic layers are brought into a ferrimagnetic state, and assuming that saturation magnetization and the thickness of the second free magnetic layer provided on the nonmagnetic conductive layer side are M2 and t2, respectively, and saturation magnetization and the thickness of the first free magnetic layer are M1 and t1, respectively, M2xc2x7t2 greater than M1xc2x7t1 is satisfied.
In the spin valve thin film magnetic element, assuming that saturation magnetization and the thickness of the second free magnetic layer of the two magnetic layers, which constitute the free magnetic layer, are M2 and t2, respectively, and saturation magnetization and the thickness of the first free magnetic layer are M1 and t1, respectively, the magnetic thicknesses of the second and first free magnetic layers are represented by M2xc2x7t2 and M1xc2x7t1, respectively.
Since the free magnetic layer of the spin valve thin film magnetic element is formed to satisfy the relation M2xc2x7t2 greater than M1xc2x7t1, the magnetic thickness of the second free magnetic layer is larger than that of the first free magnetic layer.
Therefore, the spin flopping field of the free magnetic layer is increased to stably maintain the antiferromagnetic coupling between the first and second free magnetic layers, thereby increasing the rate of change in resistance while maintaining the ferrimagnetic state of the free magnetic layer. Thus, the sensitivity of the spin valve thin film magnetic element can be increased.
Furthermore, the first and second free magnetic layers are antiferromagnetically coupled with each other to be put into the ferrimagnetic state, the magnetic effective thickness of the free magnetic layer is represented by (M2xc2x7t2xe2x88x92M1xc2x7t1).
Therefore, the effective thickness of the free magnetic layer can be decreased by appropriately controlling the magnetic thicknesses of the two magnetic layers to increase the rate of change in resistance, increasing the sensitivity of the spin valve thin film magnetic element.
Particularly, when the second free magnetic layer comprises a ferromagnetic layer and an anti-diffusion layer in order to prevent mutual diffusion between the magnetic layer on the nonmagnetic conductive layer side and the nonmagnetic conductive layer, the magnetic thickness M2xc2x7t2 of the second free magnetic layer is represented by the sum of the magnetic thicknesses of the anti-diffusion layer and the ferromagnetic layer.
Therefore, the difference (M2xc2x7t2xc2x7M1xc2x7t1) can be decreased by appropriately controlling the saturation magnetization and the thickness of each of the anti-diffusion layer, the ferromagnetic layer, and the other magnetic layer so that the magnetization direction of the free magnetic layer can be changed with an external magnetic field of small magnitude, further increasing the sensitivity of the spin valve thin film magnetic element.
Furthermore, the thickness of the free magnetic layer can be decreased by appropriately controlling the saturation magnetization and the thickness of each of the anti-diffusion layer, the ferromagnetic layer, and the first free magnetic layer to decrease a shunt (a so-called shunt loss) of a sensing current in the free magnetic layer, and increase the rate of change in resistance.
In the above-described spin valve thin film magnetic element of the present invention, the thickness of the second free magnetic layer lies in the range of 25 to 45 xc3x85.
In the spin valve thin film magnetic element, the thickness of the second free magnetic layer provided on the nonmagnetic conductive layer side lies in the range of 25 to 45 xc3x85, and thus the rate of change in resistance of the spin valve thin film magnetic element can be increased.
In the spin valve thin film magnetic element of the present invention, the pinned magnetic layer may comprise first and second pinned magnetic layers with a nonmagnetic layer provided therebetween, wherein the magnetization directions of the first and second pinned magnetic layers are antiparallel to each other, and the first and second pinned magnetic layers are put into a ferrimagneic state.
In this spin valve thin film magnetic element, the magnetization directions of the first and second pinned magnetic layers are antiparallel to each other, and the first and second pinned magnetic layers are put into the ferrimagneic state, thereby leaving slight spontaneous magnetization of the whole pinned magnetic layer. Therefore, the spontaneous magnetization can be further amplified by an exchange coupling magnetic field with the antiferromagnetic layer to strongly pin the magnetization direction of the pinned magnetic layer.
A thin film magnetic head of the present invention comprises the above-described spin valve thin film magnetic element.
The thin film magnetic head comprises the spin valve thin film magnetic element exhibiting the high rate of change in resistance and high sensitivity, and can thus detect an external magnetic field of small magnitude, increasing the reproduced output of the head. Therefore, the thin film magnetic head can be used as a magnetic recording device with a high recording density.
A method of manufacturing a spin valve thin film magnetic element of the present invention comprises the lamination step of laminating an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic conductive layer, and a free magnetic layer comprising first and second free magnetic layers antiferromagnetically coupled with each other with a nonmagnetic intermediate layer provided therebetween to form a lamination, the first heat treatment step of heat-treating the lamination with a magnetic field applied in the direction perpendicular to the track width direction of the lamination to produce an exchange coupling magnetic field between the antiferromagnetic layer and the pinned magnetic layer so that the magnetization direction of the pinned magnetic layer is pinned in the direction perpendicular to the track width direction, and the second heat treatment step of heat-treating the lamination with a magnetic field applied in the track width direction, which is higher than the coercive force of the free magnetic layer and lower than the magnetic field of spin flopping transition of the first and second free magnetic layers antiferromagnetically coupled with each other, to orient the direction of induced magnetic anisotropy of the first and second free magnetic layers in the track width direction, wherein the thickness of the second free magnetic layer provided on the nonmagnetic conductive layer side is larger than that of the first free magnetic layer.
In the present invention, the free magnetic layer comprises the first and second free magnetic layers antiferromagnetically coupled with each other, and the coercive force of the free magnetic layer means a magnetic field with which synthetic magnetization (M2xc2x7t2xe2x88x92M1xc2x7t1) is oriented in the direction of the applied magnetic field with the magnetization directions of the first and second free magnetic layers maintained in an antiparallel state.
In this method of manufacturing a spin valve thin film magnetic element of the present invention, the thickness of the second free magnetic layers of the two magnetic layers, which constitute the free magnetic layer, is larger than that of the first free magnetic layer, and the lamination is heat-treated with a magnetic field applied in the track width direction, which is higher than the coercive force of the free magnetic layer and lower than the magnetic field of spin flopping transition of the first and second free magnetic layers, to orient the direction of induced magnetic anisotropy of the first and second free magnetic layers, which is disturbed by the first heat treatment step, in the track width direction. Therefore, the spin valve thin film magnetic element exhibiting less Barkhausen noise in the free magnetic layer, high sensitivity, and the high rate of change in resistance can be obtained.
Furthermore, the method of manufacturing the above-described spin valve thin film magnetic element of the present invention may further comprise the third heat treatment step of heat-treating the lamination at a temperature lower than the heat treatment temperature of the second heat treatment step with a rotating magnetic field applied, which is higher than the coercive force of the free magnetic layer and lower than the magnetic field of spin flopping transition of the first and second free magnetic layers, after the second heat treatment step.
In this method of manufacturing the spin valve thin film magnetic element, heat treatment with the rotating magnetic field applied can decrease the magnetic hysteresis of the free magnetic layer to further decrease Barkhausen noise of the free magnetic layer, thereby producing the spin valve thin film magnetic element having high sensitivity.